Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $242.71   5.751%   $256.6683   $256.67   $256.65   $256.70  
  Purchase #2 $114.50   9.872%   $125.8034   $125.80   $125.80   $125.80  
  Purchase #3 $28.85   5.240%   $30.3617   $30.36   $30.35   $30.40  
  Purchase #4 $160.52   7.427%   $172.4418   $172.44   $172.45   $172.40  
  Purchase #5 $198.77   10.647%   $219.933   $219.93   $219.95   $219.90  
  Purchase #6 $164.33   4.844%   $172.2901   $172.29   $172.30   $172.30  
  Purchase #7 $142.45   4.522%   $148.8916   $148.89   $148.90   $148.90  
  7 purchase totals = $1,052.13       $1,126.3899   $1,126.38   $1,126.40   $1,126.40